Jerry Bransford shines his flashlight over the limestone walls of Mammoth Cave near Cave City, Ky. (pop. 1,880), as dozens of visitors cluster around him in the cool, dark expanse. The walls are scratched and gouged with the signatures of long-ago visitors and guides, and his flashlight beam stops on one name, forming a halo around the words "Mat 1850."

"Mat was the son of a wealthy Scotch-English farmer named Thomas Bransford and a slave girl named Hannah," explains Bransford, 62. "He was leased to explore this cave and guide folks through it when he was just a teenager. By 1850, Mat would have already been working in the cave for 12 years."

As Jerry Bransford turns to lead his tour group further into the shadows, one visitor continues to stare at the name etched in stone. "Was this Mat here related to you?" he asks.

Bransford smiles. "Yes, indeed. He was my great-great-grandfather."

A seasonal tour guide since 2004 at the world's longest cave system, Bransford picks up more than a flashlight every time he leads visitors through the underground passageways. He resumes a family legacy that began in 1838 when Materson "Mat" Bransford was a slave.

That year, the cave's new owner, Franklin Gorin, decided to turn the gaping hole into a tourist attraction and needed explorers to create safe, entertaining routes through the limestone cavern. He directed three young menhis own slave, Stephen Bishop, along with Mat and Nick Bransfordto map the uncharted wilderness by the light of their torches. Over the next few decades, the three crawled, leapt and inched their way through hundreds of miles of the cave and discovered many of the iconic wonders that continue to delight visitors today.

"Mat, Nick and Stephen guided the most educated people from all over the world through this cave," Bransford tells the group during his two-hour tour. "Slaves weren't allowed education, but we think they learned to read and write from these famous visitors. We find their names all over the cave."

As Mammoth Cave became known as one of the world's natural wonders, the slave guides became well known themselves. Mat Bransford's sons, grandsons and great-grandsons continued to lead cave tours into the 20th century and, in 1930, eight Bransfords worked as guides. However, when the property became a national park in 1941, none of the Bransfords or other black cave guides were hired. Most scattered far from the cave, and knowledge of their legacy faded.

Joy Lyons helped to unearth the Bransfords' contribution when she arrived at Mammoth Cave in 1979 as a seasonal guide. In those days, Bishop, who is buried near the cave's visitor center, was the only slave credited with the cave's early exploration. But Lyons realized that many of the exploits attributed to Bishop involved other slaves.

Through years of painstaking research, Lyons learned about the Bransfords and met Jerry Bransford, who at the time worked for Dow Corning Corp. in nearby Elizabethtown, Ky. (pop. 22,542). She encouraged him to become a seasonal guide and to speak to groups about his family's history. After retiring from Dow Corning in 2002, he became the first Bransford guide at Mammoth since his great-uncle Louis finished his last tour in 1939.

"Jerry helps put a face on the story," says Lyons, author of Making Their Mark: The Signature of Slavery at Mammoth Cave and the park's chief of program services. "That personal connection to the cave really touches a lot of visitors."

Among those touched is Terry Ivy, 47, of Quitman City, Miss., making his second visit to Mammoth Cave with his wife, Susanne. "I have a whole new perspective on this place," says Ivy, emerging from the dark hole and lingering at the cave's entrance to ask Bransford several questions. "You see the beauty of the cave side by side with the pain of slavery. That tension makes it so remarkable."

As he walks in his ancestors' footsteps, Jerry Bransford can't help but compare himself to Mat Bransford and other black Americans who explored Mammoth's dark labyrinth. "My job here is very moderate in comparison with theirs, because a 'short' tour in the 1840s could last 15 hours," he says. "And they were still slaves when they came to the surface. But if you had to be a slave, wouldn't you rather be escorting educated people from around the world through Mammoth Cave?"